In this grant, we propose to understand role of kinesins in axonal transport and synapse formation. Because of the extraordinary length of axons, synaptic vesicles and active zone proteins need to be transported over long distance on microtubules to reach the distal axon where synapses form. Our previous work showed that the entry and exit of synaptic cargoes into and from the kinesin transport system are important regulatory steps for control the location of synaptogenesis and the size of synapses. Here, we use genetic, biochemical, biophysical and cell biological method to directly understand how UNC-104/KIF1A is regulated in vivo to achieve specific loading and unloading of synaptic cargoes. We will also study how force generation of kinesins impacts the transport system by perturbing force generation and studying the consequence of such perturbations. We will also study how the distinct functions of two kinesins in trafficking synaptic cargoes. Through these experiments, we hope to provide mechanistic understandings of how the KIF1A family of kinesin motors is controlled in vivo. We also hope to provide insights in the biological meaning of regulated force generation. Since axonal transport defects has been recognized as early pathological progression of neurodegenerative diseases, these molecular understandings can potential lead to therapeutic innovations.